The invention relates to a device for clamping a printed circuit board module in a mounting groove of a cold plate.
A modular design has become established in industrial electronics. Electronic components such as processors, semiconductor chips, resistors and capacitors are placed on printed circuit boards having a standardized size. Several printed circuit boards are then inserted into a housing or a mounting rack and locked in place there. The rear edges of the individual printed circuit boards carry multi-pin connectors, which upon insertion are mechanically and electrically connected to corresponding connectors of a backplane in the housing or card cage.
Special, very high demands are placed on the mechanical stability and dustproofness of electronic devices for applications in rough environments, such as on ships, in airplanes, during mobile communication or in the oil and gas industry. As the performance and component density of electronics are continually on the rise, cooling the electronic components, notably the processors, poses a special challenge.
Especially stable modular systems have been developed for such special requirements, in which the electronic printed circuit boards are packed between metal plates, and the resulting printed circuit board modules are not inserted in conventional guide rails, but are mounted to special mounting plates made of solid metal. For this purpose, grooves having a rectangular cross-section are worked into the mounting plates and receive the lower edge of a printed circuit board module.
Packing the printed circuit boards in metal plates not only provides mechanical protection for the sensitive electronics, but is also used to dissipate loss to the outside. Dissipating heat from such conduction-cooled modules takes place by way of the metallic mounting plate, which is why this can also be referred to as a cold plate.
So as to achieve the necessary high mechanical stability and optimal heat dissipation, it is not sufficient to simply insert the printed circuit board modules into the mounting grooves of the cold plate and lock them in place there so as to prevent these from being inadvertently pulled out. Rather mounting takes place by way of special clamping devices, which are inserted into the mounting groove parallel to the printed circuit board module and then clamp the lower edge of the module between the walls of the mounting groove.
Clamping retainers for establishing a positive and non-positive connection between the printed circuit board module and the cold plate, while also establishing good heat-conducting contact for the purpose of heat dissipation, are known from the prior art and are offered by CALMARK Corporation, CA 91776, USA, for example, by the designation Card-Lok. Similar clamping retainers are distributed by Pentair Inc., Minneapolis, USA under the trade name BIRTCHER Wedge-Lok. U.S. Pat. No. 5,485,353 relates to such a clamping retainer.
The previously known mounting devices comprise a number of wedge-shaped pieces, which are arranged in a row on a threaded shaft and held together by the same. The wedge-shaped pieces are pulled together by a rotation of the threaded shaft, wherein at least one wedge-shaped piece gives way laterally under the pressure that is placed on the wedge surfaces thereof. The mounting device thus widens, whereby the same becomes clamped in the mounting groove of the cold plate. These and similar mounting devices comprising wedge-shaped clamping elements are described, for example, in U.S. Pat. No. 4,819,713 (corresponds to DE 3 890 343 C2), EP 0 772 380 B1 or GB 2191046 A (corresponds to DE 3 717 689 A1).
Although the aforementioned mounting devices comprising wedge elements have been successfully applied for many years, they are also associated with drawbacks, in particular in terms of the ability to remove heat from the conduction-cooled printed circuit board modules. The bevels of the wedge-shaped pieces sliding on top of each other provide only a relatively small surface through which the heat can flow. This is because the wedge-shaped pieces are not solid, but have to be designed as U profiles, so that the threaded spindle can be guided through these. Only those wedge-shaped pieces that give way laterally under the pressure of the threaded spindle are seated against the groove wall in a planar manner. As a result, on the length of these pieces is available as a contact surface for transmitting heat to the cold plate. The wedge elements displaced in the opposite direction can give off the absorbed heat to the neighboring wedge elements only via the relatively small bevel surfaces.
U.S. Pat. No. 5,859,764 discloses a clamping device comprising an elongated U-shaped housing and a wedge-shaped pressure piece (see FIG. 5), which is displaceably mounted in the housing and has a flat clamping surface at the front side. The back side of the wedge-shaped pressure piece is seated against a laterally reversed second sub-piece and the pressure piece can be displaced transversely relative thereto. A long screw penetrates the two sub-pieces and connects these to each other. When the screw is rotated, the two wedge-shaped sub-pieces are displaced relative to each other. This causes the front sub-piece to be moved through the open front side out of the U-shaped housing, wherein it must lose contact with the lateral walls of the housing. Heat transmission from the housing to the pressure element is thus no longer assured over the entire length of the pressure piece.